$ { {5} \times \left[\begin{array}{r}{0} \\ {0} \\ {3}\end{array}\right] = {?} } $
Answer: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{r}{5}\times{0} \\ {5}\times{0} \\ {5}\times{3}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{r}{0} \\ {0} \\ {15}\end{array}\right]}$